Rotary drill bits for penetrating geological formations take on all sorts of different forms. When any bit engages rock-like material, the rate of penetration becomes extremely slow, and in order to increase the rate of penetration, it is common to apply as much downward force onto the cutting face of the bit as may be practical. In order to achieve this increase in downward force on the bit, it is often necessary to employ massive steel cylinders called drill collars, or otherwise, the borehole may deviate from a straight line which results in a crooked hole.
In order to increase the rate of penetration without subjecting the drill bit to excessive downward force, the present invention provides a formation engaging face in the form of a cone having a centerline arranged at an angle respective to the centerline of the upper part or main body of the bit. The bit main body rotates while the formation engaging member remains nonrotatable so that the resultant cooperative action therebetween causes the lower member to wobble, thereby engaging the bottom of the borehole with a force which is directed mostly along a limited area of one side of the cone, with this formation engaging area traveling circumferentially about the bit face in accordance with the relative position of the two members respective to one another.
Since only a small area of the face of the lower member is urged against the formation, the downward force on the bit is distributed over a relatively small area, thereby providing an unusual large force between the cutting elements of the bit and the formation.